In the field of data processing, the use of point of sale (POS) terminals has required and also has enabled rapid and accurate transfer of information from one location to another in a business operation. In the case of department stores, the sales data must be transmitted or communicated from one or more terminals throughout the store to a central computer or processing unit.
A filing system is used to provide and maintain inventory and price data on the huge number of items that are sold in the store. The filing system and the control therefor provide means for retrieving and updating data and information regarding the constantly changing inventory and prices for the overall operation.
Representative documentation in the field of file backup systems includes Japanese Patent Specification No. 209642/87 which discloses point of sale (POS) data files provided in a master terminal and in a master backup terminal and wherein both terminals update the data files in response to a request from a satellite terminal and transmit PLU (price look up) data to the satellite terminal.
U.S. Pat. No. 4,319,326, issued to Y. Uchida on Mar. 9, 1982, discloses a plurality of electronic cash registers and a consolidator unit which includes means for storing data corresponding to data for each operator of the registers.
U.S. Pat. No. 4,590,551, issued to R. D. Mathews on May 20, 1986, discloses a master processor and a slave processor with local memory and dual memory control circuits. The two units access a common shared memory and contention is resolved by logic of the master processor.
U.S. Pat. No. 4,683,536, issued to M. Yamamoto on July 28, 1987, discloses a plurality of credit terminals and one of such terminals collects sales data from other terminals and transmits such data to the host computer.
U.S. Pat. No. 4,733,392, issued to K. Yamaguchi on Mar. 22, 1988, discloses fail memory equipment with a plurality of memory blocks which can be changed serially or in parallel for testing.
And, U.S. Pat. No. 4,771,382, issued to F. Shiono et al. on Sept. 13, 1988, discloses a master ECR for interrogating the state and data contents of a slave ECR wherein a state indicating signal exists to indicate whether a reset operation or a read operation has been conducted. The operator of the master machine can monitor the state of each slave machine.
In a conventional point of sale (POS) system, the construction is such that POS data files are provided in both a master terminal and in a backup master terminal. The master terminal is designed to update a file and to transmit data such as price look up (PLU) data and the like to a satellite terminal in response to a request from such satellite terminal. Additionally, in a conventional system, the latest sales information and the like is recorded in the POS data file, so that when any one of the files is down or destroyed, the system operation is temporarily stopped to copy data in a normally operating file to the down or destroyed file for re-preparation of such down or destroyed file. Further, it is a problem in a conventional system that when a file is down or destroyed due to failure of hardware or any other cause, the file cannot be prepared unless the system operation is stopped. In other words, when a file is down or destroyed during operation of the system, the file may not or cannot be re-prepared until the business closes even after the hardware is repaired. In this regard, the system has to operate with only one file after another file is down or has been destroyed and it is possible that the system may fail which would stop the operation if the remaining file is down or is destroyed.